Effects of grain or pasture finishing systems on carcass composition and tissue accretion rates of lambs.

The effects of finishing system on growth performance and carcass composition were determined in an experiment using 40 crossbred, early-weaned lambs (28 kg BW). Finishing systems were 1) grazed alfalfa, 2) 100% concentrate diet fed in drylot, and 3) grazed ryegrass for 42 d followed by a 100% concentrate diet fed in drylot. All lambs were fed to similar final weights (48 kg). Average daily gain was greater for lambs placed directly in the feedlot than for lambs on the other two finishing protocols. The quantity of separable lean tissue and bone were not affected by finishing system. However, quantity of total fat and each of the three major fat depot sites (subcutaneous, seam, and mesenteric) were reduced (P < .05) in alfalfa-finished lambs compared with fat in lambs fed concentrate at some time during finishing. Daily accretion rates of lean and fat tissue were greater (P < .05) for lambs placed directly in drylot than for lambs that consumed forage at some time. In addition, daily fat accretion rates were greater in lambs placed directly in drylot than in lambs that initially grazed ryegrass. Composition of individual primal cuts revealed reductions (P < .05) in total separable fat with alfalfa finishing compared with the other two systems. However, chemical composition of the lean tissue within the primal cuts was not affected by finishing system, with the exception of the loin and breast. Finishing systems based on grazed forage can lead to the production of leaner carcasses, but major differences in the composition of consumable product were not observed.